Agricultural vehicles, such as tractors, are equipped with a pivoting front axle to improve the comfort and to increase the stability of the tractor on the field. Furthermore, such a pivoting front axle assures that the rear wheels of the tractor (typically the powered wheels) are in touch with the ground surface at all times to assure a proper traction.
The main cause of tractor crashes is overturning (roll-over). When the tractor is driven over steep slopes or uneven ground, overturning can occur. Thereby, the pivoting front axle significantly decreases the stability of the tractor in an overturning situation. From a safety point of view, overturning is a big issue for agricultural vehicles with a pivoting front axle.
EP 2 444 304 describes an active anti roll-over system. Thereby, a hydraulic cylinder is placed between the pivoting front axle, and the body of the agricultural vehicle. The hydraulic cylinder is connected to a hydraulic circuit so that a predetermined force can be applied to the cylinder in a roll-over situation, to increase the stability of the agricultural vehicle. A drawback of this anti roll-over system, is that it requires power to operate the hydraulic system (a hydraulic pump is essential in the proposed system, hence the roll-over system is active). When the engine of the agricultural vehicles stalls and power is lost, then the anti roll-over protection system will not work, resulting in an unsafe situation.
EP 1 541 773 describes a passive anti roll-over system. Particularly, it describes a wheel type construction machine having a hydraulic suspension system. Thereby, the hydraulic cylinders, operating as suspension system, are connected to an accumulator (to obtain the suspension effect). When a roll-over situation is detected, the system of EP 1 541 773 cuts the connection between the cylinder and the accumulator, so that further movement of the cylinder is blocked. In this manner, a passive anti roll-over system is obtained. The anti roll-over system does not comprise a hydraulic pump that depends on external energy, and can be activated via a signal (to switch a valve). Therefore this system is operable even when the agricultural vehicle stalls and power is lost. A drawback of this passive anti roll-over system is that it is not designed for a pivoting front axle. Particularly, this passive anti roll-over system does not comprise a state wherein no force is applied to the hydraulic cylinders, which is required to allow the front axle to freely pivot.
It is an object of the present invention to provide a passive anti-rollover system to an agricultural vehicle having a pivoting front axle.